<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        /* 如果前面的元素float,后面的元素没有清除  */
     .one,.tow,.three{
         width: 100px;
         height: 100px;
     }
    .one{
        background: salmon;
            }
    .two{
        background: skyblue;
        float: left;
    }
    .three{
        background:royalblue;
        float:right;
    }
    </style>
</head>
<body>
    <div class="one"></div>
    <div class="two"></div>
    <div class="three"></div>
</body>
</html>